1. Technical Field
The present disclosure relates generally to information processing systems and, more specifically, to embodiments of a method and apparatus for selecting spawning pairs for speculative multithreading.
2. Background Art
In order to increase performance of information processing systems, such as those that include microprocessors, both hardware and software techniques have been employed. One approach that has been employed to improve processor performance is known as “multithreading.” In multithreading, an instruction stream is split into multiple instruction streams that can be executed concurrently. In software-only multithreading approaches, such as time-multiplex multithreading or switch-on-event multithreading, the multiple instruction streams are alternatively executed on the same shared processor.
Increasingly, multithreading is supported in hardware. For instance, in one approach, referred to as simultaneous multithreading (“SMT”), a single physical processor is made to appear as multiple logical processors to operating systems and user programs. Each logical processor maintains a complete set of the architecture state, but nearly all other resources of the physical processor, such as caches, execution units, branch predictors, control logic, and buses are shared. In another approach, processors in a multi-processor system, such as a chip multiprocessor (“CMP”) system, may each act on one of the multiple threads concurrently. In the SMT and CMP multithreading approaches, threads execute concurrently and make better use of shared resources than time-multiplex multithreading or switch-on-event multithreading.
For those systems, such as CMP and SMT multithreading systems, that provide hardware support for multiple threads, several independent threads may be executed concurrently. In addition, however, such systems may also be utilized to increase the throughput for single-threaded applications. That is, one or more thread contexts may be idle during execution of a single-threaded application. Utilizing otherwise idle thread contexts to speculatively parallelize the single-threaded application can increase speed of execution and throughput for the single-threaded application.